Upgrade from SQL Server 2008R2 RTM to 2008R2 SP3

Hi all,

In my environment we are using SQL server 2008r2 RTM version.Recently we are facing some issues.So, we are planning to upgrade sercvice pack 3(SP3).

Current version i am using:

Microsoft SQL Server 2008 R2 (RTM) - 10.50.1600.1 (X64)   Apr  2 2010 15:48:46   Copyright (c) Microsoft Corporation  Enterprise Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1) (Hypervisor) 

My Questions are

1.Is this directly upgrade from SQL Server 2008R2 RTM to 2008R2 SP3 or not? otherwise how to upgrade ?

2.what is the procedure  upgrade from SQL Server 2008R2 RTM to 2008R2 SP3 in SQL 2008 cluseter environment.

Please provide solution.

Thank you,

Raj